9

406 Chapter 12: Animation
Look A t Constr ai nt
Animation menu > Constraints > LookAt Constraint
LookAt con straints enable the antenna dishes to track the
satellite.
The LookAt constraint controls an object’s
orientation so that it’s always looking at another
object. It locks an object’s rotation so that one of its
axes points toward the target object. The LookAt
axis points toward the target, while the Upnode
axis defines w hich axis points upward. If the two
coincide, a flipping behavior may result. This is
similar to pointing a target camera straight up.
An example of a LookAt constraint’s use would be
to constrain the eyeballs of a character to a point
helper. The eyes will then always be aimed at the
point helper. Animate the point helper, and the
eyes follow. Even if you rotate the character’s head,
the eyes maintain their lock on the point helper.
Multiple Tar gets and Weighting
A constrained object can be influenced by several
target objects. When using multiple targets, ea ch
targethasaweightvaluethatdefinesthedegreeby
which it influences the constrained object, relative
to other targets.
Using Weight is meaningful (and available) only
w ith multiple targets. A value of 0 means the
target has no influence. Any value greater than
0 causes the target to influence the constrained
object relative to other t argets’ Weight sett ings.
For example, a target with a Weight va lue of 80 will
have twice the influence of a target with a Weight
value of 40.
Procedures
To a ssign a Look At constrai nt:
1.
Select the object you want to constrain. This
istheobjectthatwillbealwayslookingatits
target.
2. Choose Animation menu > Constraints >
LookAt Constraint.
3. Select the target object.
To access the LookAt constraint ’s parameters
through the Motion panel:
1.
Select the LookAt C onstrained object.
2. On the Motion panel > Rotation list,
double-click LookAt Constraint.
The Lo okAt constraint parameters are located
under the LookAt Constraint rollout.
To edit weight values:
1.
Select the constrained object.
2. On the Motion panel > Rotation list,
double-click LookAt Constraint.
The Lo okAt constraint parameters are located
under the LookAt Constraint rollout.
3. Click a target from the list.
4. UsetheWeightspinnerorenteranumerical
value to adjust the weight value.
To animate weight values:
1.
Select the constrained object.
2. On the Motion panel > Rotation list,
double-click LookAt Constraint.
The Lo okAt constraint parameters are located
under the LookAt Constraint rollout.